The present invention relates to an antistatic shelf for supporting electronic circuit boards, and more particularly to such a shelf which can be adjustably mounted in a storage cabinet or container.
Circuit boards, such as those used by the telecommunication and electronic industries, contain expensive solid state and microelectronic components which are extremely sensitive to static electricity. Often, such boards can run in the thousands or tens of thousands of dollars each, yet can be destroyed by transient static charges such as those which sometimes jump from a person's hand to a metal handrail or the like under conditions of low humidity. Such circuit boards can also be destroyed by the uncontrolled, rapid discharge of components thereon after removal of the boards from active service in a computer, switching system, or the like. It is therefore necessary to protect such circuit boards against ambient static charges and against rapid discharge of the components on the circuit board.
Prior solutions to the static and discharge problems have centered around containers for the circuit boards, such as plastic bags or cartons, which are rendered conductive with an appropriate antistatic agent. Chemical agents for providing antistatic properties are disclosed, for example, in U.S. Pat. No. 3,405,001. Examples of known antistatic containers for electronic parts are provided in U.S. Pat. Nos. 4,293,070 and 4,231,901. The '070 patent discloses a container composed entirely of paperboard coated on the inside surfaces with conductive carbon black particles to prevent an outside static electricity charge from passing through the container. In the '901 patent, a urethane foam having electrically conductive properties is used to wrap electronic components to protect them from static charge. The foam contains a binding agent and is impregnated generally uniformly therethrough with an electrically conductive amount of an electrically conductive particulate material, e.g. carbon-black, silver, aluminum, or a metal salt. U.S. Pat. No. 4,223,368 discloses an electrostatic discharge protection device adapted to be clipped onto edge connectors of a circuit card assembly. The device includes a shunt for electrically short circuiting the edge connectors of the card.
When removing circuit cards from electronic mainframes, it is inconvenient to re-package the boards in individual storage containers such as the cartons or bags described above. However, it is imperative that such boards be stored, for future use, in a manner which will protect them against damage from electrostatic discharge. It would therefore be advantageous to provide a storage facility, such as a cabinet or other container, into which the circuit boards can be placed for convenient retrieval when needed, and which protects the circuit boards and the components thereon from damage due to electrostatic discharge. Such a cabinet should provide flexibility in terms of the types and sizes of circuit boards which it can accomodate.
The present invention relates to an adjustable antistatic shelf for such a storage cabinet or like container.